The conversion of starch to glucose generally is effected in two discrete processes. Initially the starch is partially hydrolyzed, either by acid or by enzymes. The partially hydrolyzed starch (starch hydrolysate, thinned starch) typically contains only a few percent glucose and is the substrate for amyloglucosidase (glucoamylase), hereafter denoted AG, an enzyme which completes the hydrolysis of polysaccharides to glucose.
The most commonly utilized source of AG is microorganisms from the genus Aspergillus, and the AG catalyzed hydrolysis of thinned starch is most commonly performed batchwise. When considering continuous methods of hydrolyzing thinned starch, especially those where the enzyme is to be reused, it soon becomes apparent that thermostability of AG is an important factor for several reasons. One reason is that the higher its thermostability, the longer will be the enzyme lifetime, hence the greater will be its effective utilization. Another factor is the higher productivity per unit time resulting from higher temperatures. Yet another factor is that microbial contamination is reduced at higher temperature.
U.S. Pat. No. 4,247,637 describes a thermostable AG elaborated by a microorganism isolated from the soil and identified as Talaromyces duponti. This application describes an AG remarkably more thermostable than that disclosed above.